Can anyone explain to me...

With the weather so brilliantly mild the past few days (low humidity and temps only in the 80s), I've had the front door and all the windows open. The ice cream trucks are on their summer rounds and their little recorded music "mixes" have been drifting in my open windows. What I'd like to know is, why on earth are they playing Christmas carols in the middle of summer?!? I'm not talking "Frosty the Snowman" either; they're playing "Silent Night" and "God Rest ye Merry, Gentlemen"!